The drive for miniaturisation to the submicron level within the field of electronics necessitates constant improvements in lithographic processing. Nano-imprint lithography (NIL) is a promising lithographic technique for producing nanometer-sized structures in a parallel process. NIL has been adapted on the International Technology Roadmap for Semiconductors (IRTS) as a potential lithographic technique in order to meet the target of a 32-nm node in 2013. However, a number of technical problems related to NIL have to be solved first, such as: homogeneity of large imprint areas, sub-micron alignment, error detection, cycle time, and critical dimension control.
In Microelectronic Eng. 73-74 (2004) p. 167-171, Plachetka et al. discloses a NIL process based on ultraviolet (UV) curable resists. In this UV-NIL process, a flexible transparent stamp fabricated of polydimethylsiloxane (PDMS) ensures a conform contact to the UV-curable resist coated on a substrate. Due to the elastomeric character of the PDMS the stamp adapts its shape to the waviness of the substrate and the lack of parallelism between the substrate and the stamp is solved in this way.
US2003/0017424 discloses a technique intended for forming patterns, such as grating structures on semiconductor substrates and other structures. Thus, this reference describes an imprint master (stamp) that may be rigid or mechanically flexible. For creation of the pattern the imprint master is pressed against a substrate coated with a deformable viscous or liquid material. The imprint master may be a composite member including a fixed medium (imprinting section) and a bulk material (back part). The fixed medium includes the imprint pattern and may be formed of a hard material, such as silicon, or it may be formed of a mechanically flexible material, such as PDMS. The bulk material may similarly be formed of a hard material, such as silicon or glass that may have been formed thin enough to be somewhat bendable, or it may be formed of a mechanically flexible material, such as PDMS.
However, a problem for stamps made of an elastomeric material is that during imprinting the stamp will be deformed in a direction perpendicular to the imprinting direction due to a relatively high Poisson's ratio of the stamp material. This may cause an undesirable stretching or distortion of the lithographic pattern of the stamp. Therefore, the applied pressure on the stamp of Plachetka et al. and the flexible stamps of US2003/0017424 are effectively limited to a low range of pressures. Moreover, relatively large but local imperfections in or on the substrate may influence neighbouring imprinting sections of such a stamp.
US 2002/0132482 discloses a method of imprint lithography using a fluid pressure to press a mould (stamp) into a substrate-supported film. The mould consists of a body and a moulding layer that are typically made of hard materials such as fused quarts, glass or ceramic. The substrate comprises a semiconductor wafer and the substrate-supported film can be a polymer such as PMMA or it can be a liquid, such as UV-curable silicone. The mould body and/or the substrate are made flexible by using silicon substrates with a thickness less than 2 mm. Thereby the mould and substrate will conform despite deviations from planarity. The pressure used during the imprinting process is within the range 1-1000 psi=6.9 kPa−6.9 MPa.
However, the stamps of US 2002/0132482 suffer from the inherent disadvantage that the bending of the mould/substrate the imprinting will inevitably result in an inhomogeneous imprinting pressure, which may in turn seriously deteriorate the formed lithographic pattern.
Hence, an improved stamp for NIL would be advantageous, and in particular a more flexible stamp would be advantageous.